Abstract:

A gear pump includes: a drive shaft; a first gear; a second gear; a first
plate disposed between the first gear and the second gear, and arranged
to liquid-tightly seal the first surfaces of the first and second gear; a
pair of second plates disposed, respectively, on the second surfaces of
the first and second gears, and arranged to liquid-tightly seal the
second surfaces of the first and second gears, each of the second plates
including a tooth top sealing portion having a seal surface arranged to
seal a tooth top of the first gear and a tooth top of the second gear,
and to form a suction portion with the first plate and the second plate;
and an urging member arranged to urge the drive shaft toward the seal
surface of the tooth top sealing portion of one of the first and second
plates.

Claims:

1. A gear pump comprising:a drive shaft driven by a driving source;a first
gear arranged to rotate integrally with the drive shaft, and to form a
first pump, the first gear having a first surface and a second surface
opposite to the first surface of the first gear;a second gear arranged to
rotate integrally with the drive shaft, and to form a second pump, the
second gear having a first surface and a second surface opposite to the
first surface of the second gear;a first plate disposed between the first
gear and the second gear, and arranged to liquid-tightly seal the first
surface of the first gear, and to liquid-tightly seal the first surface
of the second gear;a pair of second plates disposed, respectively, on the
second surface of the first gear and the second surface of the second
gear, and arranged to liquid-tightly seal the second surface of the first
gear and the second surface of the second gear, each of the second plates
including a tooth top sealing portion having a seal surface arranged to
seal a tooth top of the first gear and a tooth top of the second gear,
and to form a suction portion with the first plate and the second plate;
andan urging member arranged to urge the drive shaft toward the seal
surface of the tooth top sealing portion of one of the first and second
plates.

2. The gear pump as claimed in claim 1, wherein the first plate includes a
through hole through which the drive shaft penetrates; the drive shaft is
supported through a bearing member by the through hole of the first
plate; and the urging section is provided within the through hole of the
first plate.

3. The gear pump as claimed in claim 2, wherein the urging section is
arranged to urge the drive shaft so that the drive shaft has a center
deviated from a center of the bearing member.

4. The gear pump as claimed in claim 2, wherein the drive shaft includes a
bearing member mounting portion located on an outer circumference surface
of the drive shaft, and arranged to receive the bearing member, and an
urging member mounting portion arranged to receive the urging member.

5. The gear pump as claimed in claim 4, wherein the urging member mounting
portion includes an urging member fitting portion formed by decreasing a
diameter of the drive shaft.

6. The gear pump as claimed in claim 5, wherein the gear pump further
comprises a second bearing member which supports the drive shaft, and
which is fit in the urging member fitting portion, and positioned in an
axial direction so that the second bearing member has a center deviated
from the center of the drive shaft; the urging member is a spring member
arranged to urge the drive shaft through the second bearing member toward
the seal surface of the tooth top seal member.

7. The gear pump as claimed in claim 6, wherein the second bearing member
is positioned by the spring member in the through hole in the rotational
direction.

8. The gear pump as claimed in claim 2, wherein the gear pump further
comprises a pair of the urging members each arranged to urge the drive
shaft toward the seal surface of the tooth top sealing portion of one of
the second plates; and the drive shaft includes a bearing member mounting
portion disposed on an outer circumference of the drive shaft, and
arranged to receive the bearing member, and a pair of urging member
mounting portions disposed on both sides of the bearing member mounting
portion, and each arranged to receive one of the urging members.

9. The gear pump as claimed in claim 8, wherein the gear pump further
comprises a pair of second bearing members each of which supports the
drive shaft, and each of which is fit in one of the urging member fitting
portions, and positioned in an axial direction so that the second bearing
member has a center apart from the center of the drive shaft; and each of
the urging members is a spring member arranged to urge the drive shaft
through the second bearing member toward the seal surface of the tooth
top sealing portion.

10. The gear pump as claimed in claim 2, wherein the gear pump further
comprises a shaft seal member disposed in the through hole of the first
plate, and arranged to liquid-tightly seal between a first pump's side of
the through hole and a second pump's side of the through hole; and the
through hole of the first plate includes an annular holding groove having
a center deviated from a center of the through hole, and supporting the
shaft seal member; and the urging section is the shaft seal member.

11. The gear pump as claimed in claim 2, wherein the gear pump further
comprises a pressing member which is the urging member, which is disposed
in an inner circumference surface of the through hole of the first plate,
and which is arranged to press the drive shaft to the seal surface of the
tooth top sealing portion.

12. The gear pump as claimed in claim 11, wherein the pressing member is a
press-fitting member which is press-fit in the inner circumference
surface of the through hole of the first plate.

13. A gear pump comprising:a drive shaft driven by a driving source;a gear
disposed in a pump chamber formed in a housing, and arranged to be driven
by the drive shaft, and to form a pump;a plate disposed adjacent to a
surface of the gear, and arranged to suppress a leakage of a hydraulic
fluid from the surfaces of the gear;a tooth top seal member including a
seal surface abutted on the plate, and arranged to seal a tooth top of
the gear, and to separate the pump chamber into a low pressure portion
and a high pressure portion; andan urging member arranged to urge the
drive shaft toward the seal surface of the tooth top seal member.

14. The gear pump as claimed in claim 13, wherein the plate includes a
holding hole arranged to hold the drive shaft; and the urging member is
disposed in the holding hole of the plate.

15. The gear pump as claimed in claim 14, wherein the urging member is
supported through a bearing member by the holding hole of the plate; and
the urging member is arranged to urge the drive shaft so that the drive
shaft has a center deviated from a center of the bearing member.

16. The gear pump as claimed in claim 15, wherein the drive shaft includes
a bearing member mounting portion disposed on an outer circumference
surface of the drive shaft, and arranged to receive the bearing member,
and an urging member mounting portion arranged to receive the urging
member; and the drive shaft is positioned by the urging member mounting
portion with respect to the plate in the axial direction.

17. The gear pump as claimed in claim 16, wherein the urging member
mounting portion includes an urging member fitting portion formed by
decreasing a diameter of the drive shaft; and the gear pump further
comprises a second bearing member which supports the drive shaft, which
is fit in the urging member fitting portion, and positioned in the axial
direction so that the second bearing member has a center apart from the
center of the drive shaft; and the urging member is a spring member
arranged to urge the drive shaft through the second bearing member toward
the seal surface of the tooth top sealing member.

18. A gear pump for a brake apparatus, the gear pump comprising:a drive
shaft driven by a driving source;a first gear formed integrally with the
drive shaft, and arranged to rotate with the drive shaft, and to form a
first pump, the first gear being provided in a first brake circuit, and
having a first surface and a second surface opposite to the first surface
of the first gear;a second gear formed integrally with the drive shaft,
and arranged to rotate with the drive shaft, and to form a second pump,
the second gear being provided in a second brake circuit, and having a
first surface and a second surface opposite to the first surface of the
second gear;a seal plate disposed between the first gear and the second
gear, the seal plate including a through hole through which the drive
shaft penetrates, the seal plate being arranged to suppress a leakage of
a brake fluid from the first surface of the first gear and a leakage of a
brake fluid from the first surface of the second gear;a pair of side
plates disposed, respectively, adjacent to the second surface of the
first gear and the second surface of the second gear, and arranged to
suppress the leakage of the brake fluid from the second surface of the
first gear and the leakage of the brake fluid from the second surface of
the second gear;a tooth top sealing member including a seal surface
arranged to seal a tooth top of the first gear and a tooth top of the
second gear, and defining a low pressure portion with the seal plate and
the side plate;a bearing member mounted in the through hole of the seal
plate, and arranged to support the drive shaft; andan urging member
arranged to urge the drive shaft so that a center of the drive shaft is
eccentric in a direction from a center of the bearing member to the seal
surface of the tooth top sealing portion.

19. The gear pump as claimed in claim 18, wherein the drive shaft includes
a bearing member mounting portion disposed on an outer circumference of
the drive shaft, and arranged to receive the bearing member, and an
urging member mounting portion arranged to receive the urging member; the
urging member mounting portion includes an urging member fitting portion
formed by decreasing a diameter of the drive shaft; and gear pump further
comprises a second bearing member which supports the drive shaft, and
which is fit in the urging member fitting portion, and positioned in an
axial direction so that the second bearing member has a center deviated
from the center of the drive shaft; and the urging member is a spring
member arranged to urge the drive shaft through the second bearing member
toward the seal surface of the tooth top sealing portion.

20. The gear pump as claimed in claim 18, wherein the gear includes a
drive gear arranged to be driven by the drive shaft, and a driven gear
engaged with the drive gear, and arranged to be driven by the drive gear;
and the gear is an external gear.

Description:

BACKGROUND OF THE INVENTION

[0001]This invention relates to a gear pump and a gear pump for a brake
apparatus.

[0002]A Japanese Patent Application Publication No. 2002-70755 discloses a
conventional gear pump. This gear pump is arranged to slidably contact a
tooth top of a gear on a seal surface of a seal plate by using a pressure
difference between a high pressure side and a low pressure side of a pump
chamber, and thereby to ensure a sealing ability of the tooth top of the
gear.

SUMMARY OF THE INVENTION

[0003]However, in the above-described conventional gear pump, the tooth
top of the gear can not sufficiently contact the seal surface at an
initial stage of driving of the gear pump at which the sufficient
pressure difference between the high pressure side and the low pressure
side of the pump chamber can not be obtained. With this, it is not
possible to sufficiently increase the pressure of the gear pump.

[0004]It is an object of the present invention to provide a gear pump
devised to solve the above mentioned problem, and to sufficiently
increase a pressure of the gear pump even when a sufficient pressure
difference between the high pressure side and the low pressure side of
the pump chamber is not obtained.

[0005]According to one aspect of the present invention, a gear pump
comprises: a drive shaft driven by a driving source; a first gear
arranged to rotate integrally with the drive shaft, and to form a first
pump, the first gear having a first surface and a second surface opposite
to the first surface of the first gear; a second gear arranged to rotate
integrally with the drive shaft, and to form a second pump, the second
gear having a first surface and a second surface opposite to the first
surface of the second gear; a first plate disposed between the first gear
and the second gear, and arranged to liquid-tightly seal the first
surface of the first gear, and to liquid-tightly seal the first surface
of the second gear; a pair of second plates disposed, respectively, on
the second surface of the first gear and the second surface of the second
gear, and arranged to liquid-tightly seal the second surface of the first
gear and the second surface of the second gear, each of the second plates
including a tooth top sealing portion having a seal surface arranged to
seal a tooth top of the first gear and a tooth top of the second gear,
and to form a suction portion with the first plate and the second plate;
and an urging member arranged to urge the drive shaft toward the seal
surface of the tooth top sealing portion of one of the first and second
plates.

[0006]According to another aspect of the invention, a gear pump comprises:
a drive shaft driven by a driving source; a gear disposed in a pump
chamber formed in a housing, and arranged to be driven by the drive
shaft, and to form a pump; a plate disposed adjacent to a surface of the
gear, and arranged to suppress a leakage of a hydraulic fluid from the
surfaces of the gear; a tooth top seal member including a seal surface
abutted on the plate, and arranged to seal a tooth top of the gear, and
to separate the pump chamber into a low pressure portion and a high
pressure portion; and an urging member arranged to urge the drive shaft
toward the seal surface of the tooth top seal member.

[0007]According to still another aspect of the invention, a gear pump for
a brake apparatus, the gear pump comprises: a drive shaft driven by a
driving source; a first gear formed integrally with the drive shaft, and
arranged to rotate with the drive shaft, and to form a first pump, the
first gear being provided in a first brake circuit, and having a first
surface and a second surface opposite to the first surface of the first
gear; a second gear formed integrally with the drive shaft, and arranged
to rotate with the drive shaft, and to form a second pump, the second
gear being provided in a second brake circuit, and having a first surface
and a second surface opposite to the first surface of the second gear; a
seal plate disposed between the first gear and the second gear, the seal
plate including a through hole through which the drive shaft penetrates,
the seal plate being arranged to suppress a leakage of a brake fluid from
the first surface of the first gear and a leakage of a brake fluid from
the first surface of the second gear; a pair of side plates disposed,
respectively, adjacent to the second surface of the first gear and the
second surface of the second gear, and arranged to suppress the leakage
of the brake fluid from the second surface of the first gear and the
leakage of the brake fluid from the second surface of the second gear; a
tooth top sealing member including a seal surface arranged to seal a
tooth top of the first gear and a tooth top of the second gear, and
defining a low pressure portion with the seal plate and the side plate; a
bearing member mounted in the through hole of the seal plate, and
arranged to support the drive shaft; and an urging member arranged to
urge the drive shaft so that a center of the drive shaft is eccentric in
a direction from a center of the bearing member to the seal surface of
the tooth top sealing portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a front view showing a gear pump according to a first
embodiment of the present invention.

[0009]FIG. 2 is a sectional view taken along a section line A2-A2 of FIG.
1.

[0011]FIG. 4 is an enlarged sectional view taken along a section line
A4-A4 of FIG. 1.

[0012]FIG. 5 is a front perspective view showing a seal member of the gear
pump of FIG. 1.

[0013]FIG. 6 is a front view showing the seal member of the gear pump of
FIG. 1.

[0014]FIG. 7 is a rear view showing the seal member of the gear pump of
FIG. 1.

[0015]FIG. 8 is a front perspective view showing a first side plate of the
gear pump of FIG. 1.

[0016]FIG. 9 is a front perspective view showing the first side plate of
the gear pump of FIG. 1.

[0017]FIG. 10 is a rear view showing the first side plate of the gear pump
of FIG. 1.

[0018]FIG. 11 is a view illustrating an arrangement of the first side
plate and the first gear of the gear pump of FIG. 1.

[0019]FIG. 12 is a view illustrating an arrangement of the gear, the side
plate and the seal member of the gear pump of FIG. 1.

[0020]FIG. 13 is a sectional view taken along a section line A13-A13 of
FIG. 12.

[0021]FIG. 14A is a view illustrating a state before the gear pump of FIG.
1 and a motor are connected. FIG. 14B is a view illustrating a state
after the gear pump of FIG. 1 and the motor are connected.

[0022]FIG. 15 is an exploded perspective view showing a seal section, a
support section and an urging section of a drive shaft of the gear pump
of FIG. 1.

[0023]FIG. 16 is an enlarged sectional view showing main parts including
the seal section, the support section and the urging section of the drive
shaft.

[0024]FIG. 17 is a perspective view showing a spring member of the gear
pump of FIG. 1.

[0025]FIG. 18 is a sectional view taken along a section line A18-A18 of
FIG. 16.

[0026]FIG. 19 is a schematic view illustrating a state in which a tooth
top of the gear of the gear pump of FIG. 1 is disposed outside an
R-portion.

[0027]FIG. 20 is a schematic view illustrating a state in which the tooth
top of the gear of the gear pump of FIG. 1 is disposed inside the
R-portion.

[0028]FIG. 21 is an enlarged sectional view showing main parts including a
seal section, a support section and an urging section of a drive shaft of
a gear pump according to a second embodiment of the present invention.

[0029]FIG. 22 is an enlarged sectional view showing main parts of a seal
section, a support section and an urging section of a drive shaft of a
gear pump according to a third embodiment of the present invention.

[0030]FIG. 23 is an view illustrating the urging section of the drive
shaft of the gear pump of FIG. 22.

[0031]FIG. 24 is a sectional view illustrating a gear pump according to a
fourth embodiment of the present invention.

[0032]FIG. 25 is a sectional view illustrating a gear pump according to a
fifth embodiment of the present invention.

[0033]FIG. 26 is a sectional view which illustrates a gear pump according
to a sixth embodiment of the present invention, and which is taken along
a section line A26-A26 of FIG. 27.

[0034]FIG. 27 is a sectional view illustrating gears of the gear pump of
FIG. 26.

[0035]FIG. 28 is a sectional view illustrating a case in which a suction
operation and a discharge operation of the gear pump of FIG. 26 are
varied.

[0036]FIG. 29 is an enlarged sectional view showing main parts including a
seal section, a support section and an urging section of a drive shaft of
a gear pump according to another embodiment of the present invention.

[0037]FIG. 30 is an enlarged sectional view showing main parts including a
seal section, a support section and an urging section of a drive shaft of
a gear pump according to still another embodiment of the present
invention.

[0038]FIG. 31 is an enlarged sectional view showing main parts including a
seal section, a support section and an urging section of a drive shaft of
a gear pump according to still another embodiment of the present
invention.

DETAILED DESCRIPTION OF THE INVENTION

[0039]Hereinafter, embodiments according to the present invention is
illustrated with reference to the drawings.

[0040]Hereinafter, a first embodiment of the present invention is
illustrated. As shown in FIGS. 1 and 2, a gear pump 1 according to the
first embodiment is used as an actuator for a brake pressure control
system of a vehicle. Gear pump 1 includes a housing 2, and a pump
assembly 3 received in housing 2.

[0041][Housing] Next, housing 2 is illustrated. Housing 2 is a
substantially rectangular shape. Housing 2 includes a plurality of mount
holes 2a which are formed in outside surfaces, and to which selector
valves and sensors (not shown) are mounted. Housing 2 includes a pump
chamber 4 which is formed at a substantially central position of housing
2, which is recessed into a substantially cylindrical shape, which has
stepped portions having different diameters, and which receives the pump
assembly 3.

[0042][Pump Assembly] Next, pump assembly 3 is illustrated. An open side
of pump chamber 4 (the side of a second pump 9 described later) is a
front side (lower side of FIG. 3). A bottom side of pump chamber 4 (the
side of a first pump 8 described later) is a rear side (upper side of
FIG. 3). As shown in FIGS. 3 and 4, pump assembly 3 includes a plug
member 5, a cover member 6, a seal member 7, a first pump 8, a second
pump 9 and so on. Plug member 5 is formed into a substantially circular
disc. Plug member 5 includes a hexagonal through hole 5a which is formed
in a substantially central portion of plug member 5, and which penetrates
plug member 5. Plug member 5 includes a rear surface 5d which is formed
on a rear end portion of plug member 5, and which abuts on cover member 6
described later; and an annular protrusion 5b surrounding rear surface
5d, and projecting in the rearward direction. Moreover, plug member 5
includes an externally threaded portion 5c formed on an outer
circumferential surface of plug member 5. Externally threaded portion 5c
is screwed into an internally threaded portion 4c formed on an inner
circumferential surface of pump chamber 4. Cover member 6 is formed into
a substantially circular disc. Cover member 6 includes a front surface 6e
abutting on plug member 5, and a stepped portion 6f which is cut around
an outer circumferential surface of front surface 6e. Front surface 6e is
pushed rearwards by an axial force of plug member 5 when plug member 5 is
screwed into pump chamber 4, and consequently front surface 6e of cover
member 6 abuts on rear surface 5d of plug member 5. Plug member 5 is
disposed at a predetermined position in a state in which annular
projection 5b of plug member 5 is fit over stepped portion 6f. Cover
member 6 includes a raised portion fig which is formed on an outer
circumferential surface of cover member 6, and which has an outside
diameter substantially identical to that of an inside diameter of pump
chamber 4, and an outside diameter of annular projection 5b. Moreover,
cover member 6 includes a seal groove 6h formed on the outer
circumferential surface of cover member 6 on the rear side of raised
portion 6g. An annular seal S1 is disposed between raised portion 6g and
annular projection 5b so as to seal a clearance between cover member 6
and the inner circumferential surface of pump chamber 4. An annular seal
S2 is disposed in seal groove 6h so as to seal a clearance between cover
member 6 and the inner circumferential surface of pump chamber 4. That
is, seals S1 and S2 are mounted, respectively, at positions away from
each other in the forward and rearward directions (in the upward and
downward directions of FIG. 3). A stepped through hole 6b is formed at an
eccentric position of cover member 6. Stepped through hole 6b includes a
larger diameter (front) portion and a smaller diameter (rear) portion
having an inside diameter smaller than the inside diameter of the larger
diameter portion. A drive shaft 10 is inserted in this stepped through
hole 6b with a clearance 6a in the smaller diameter portion. Annular
seals S3 are disposed, respectively, in the larger diameter portion and
the smaller diameter portion of stepped through hole 6b to seal a
clearance around drive shaft 10. Cover member 6 further includes a
cylindrical recessed portion 6d recessed from the rear surface of cover
member 6 toward the front surface, and an annular axial projection 6c
surrounding the recessed portion 6d, and projecting axially rearwards. In
annular projection 6c, there is formed a stepped portion 6i which is cut
around the inner circumference surface.

[0043]As shown in FIGS. 5-7, seal member 7 is formed into a substantially
circular disc. Seal member 7 includes a through shaft hole 7a penetrating
in the thickness direction of seal member 7, and having a circular cross
section; and shaft holes 7b and 7c which are formed, respectively, on
front and rear surfaces of seal member 7 below shaft hole 7a, each of
which is a recessed portion having a predetermined depth, and each of
which has a circular cross section. Seal member 7 includes side seal
portions 7d which formed, respectively, on front and rear surfaces of
seal member 7 around shaft holes 7a, 7b and 7c, and which project,
respectively, in the axial direction. Seal member 7 includes a pair of
R-portions 7e, 7f protruding, respectively, from side portions of side
seal portions 7d in sideways directions. As shown in FIG. 7, on the rear
surface of seal member 7, there is formed a receiving portion 7g which
has a large diameter, and which is disposed coaxially with shaft hole 7a.
Seal member 7 includes a retaining recessed portion 7j formed at a
position to confront R-portion 7e, and recessed in the radially outward
direction. Seal member 7 includes an annular seal receiving groove 7h
formed on the outer circumferential surface of seal member 7, and
recessed in the radially inward direction. Seal member 7 includes an
annular projection 7i which is formed at a front end portion of seal
member 7, and which projects in the forward direction.

[0044]As shown in FIGS. 3 and 4, seal member 7 is pushed in the rearward
direction through cover member 6 by the axial force produced by the plug
member 5 when plug member 5 is screwed into pump chamber 4. As a result,
annular projection 7i of seal member 7 is fit in stepped portion 6i of
cover member 6. An outer region of the rear surface of seal member 7
abuts on stepped portion 4b of pump chamber 4, so that seal member 7 is
positioned reliably at a predetermined position. Drive shaft 10 is
inserted into and disposed in shaft hole 7a of seal member 7. Driven
shafts 11 are inserted into and disposed, respectively, in shaft holes 7b
and 7c. An annular seal S4 is mounted in seal receiving groove 7h of seal
member 7 to secure a sealing separation between first pump chamber P1 and
second pump chamber P2. First pump chamber P1 is formed between seal
member 7 and an annular recessed portion 4c recessed rearwards from
stepped portion 4b of pump chamber 4. First pump chamber P1 is a closed
space. First pump 8 is disposed in first pump chamber P1. On the other
hand, second pump chamber P2 is formed between recessed portion 6d of
cover member 6 and seal member 7. Second pump chamber P2 is a closed
space. Second pump 9 is disposed in second pump chamber P2. First pump 8
includes a first gear 15 having front and rear surfaces and tooth tops
sealed by seal member 7 and first side plate 14.

[0045]First, first side plate 14 is illustrated. As shown in FIGS. 8-10,
first side plate 14 is made from a resin, and formed into a substantially
triangular shape as viewed from the front direction. First side plate 14
includes three through holes 14a, 14b and 14c which are located,
respectively, near apexes of the triangle of first side plate 14, and
which penetrate first side plate 14. First side plate 14 includes a side
seal portion 14d which is formed on a front surface of first side plate
14 around through holes 14a and 14b, and which protrudes in the forward
direction. First side plate 14 includes a substantially triangular seal
block 14e which is formed on the front surface of first side plate 14,
and which protrudes in the forward direction. Seal block 14e includes a
passage portion 14f forming an opening portion extending continuously
from through hole 14c toward the center of first side plate 14; a pair of
tooth top seal portions 14g, 14h which are formed on both sides of the
passage portion 14f, and which have curved seal surfaces continuous with
parts of the side seal portion 14d; and engagement portions 14i located
on the front side of the respective tooth top seal portions 14g, 14h.
Seal block 14e further includes a groove 14j recessed inwards to surround
through hole 14c from the outer circumference of tooth top portions 14g
and 14h. As shown in FIG. 10, first side seal plate 14 includes a seal
receiving groove 14k which is formed on the rear surface of first side
plate 14, which extends curvedly so as to describe a triangle, and which
surrounds the three through holes 14a, 14b and 14c.

[0046]As shown in FIG. 4, drive shaft 10 is rotatably inserted into
through hole 14a of first side plate 14 with a predetermined radial
clearance. On the other hand, driven shaft 11 is inserted into through
hole 14b of first side plate 14 with a predetermined radial clearance.
Moreover, a seal S5 is received in seal receiving groove 14k of first
side plate 14 to secure a sealing separation between the low pressure
side and the high pressure side of first pump chamber P1.

[0047]Next, first gear 15 is illustrated. As shown in FIG. 11, first gear
(or gearing) 15 includes a driver gear 16 into which drive shaft 10 is
inserted, and a driven gear 17 into which driven shaft 11 is inserted.
Tooth tops 16a of drive gear 16 and Tooth tops 17a of driven gear 17 are
engaged with each other at a tooth engaging portion 18. Drive shaft 10
includes a recessed portion 10a recessed inwards, and located at a
position corresponding to drive gear 16. A cylindrical drive pin 10b is
received in this recessed portion 10a. Drive pin 10a extends from a
center of drive shaft 10 in the radial direction. Drive pin 10b includes
a first end received in recessed portion 10a of drive shaft 10, and a
second end engaged with a recessed portion 16b which is recessed radially
outwards from the inner circumferential surface of drive gear 16. On the
other hand, driven shaft 11 includes a recessed portion 11a recessed
inwards, and located at a position corresponding to driven gear 17. A
cylindrical driven pin 11b is received in this recessed portion 11a.
Driven pin 11b extends from a center of driven shaft 11 in the radial
direction. Driven pin 11b includes a first end received in recessed
portion 11a of driven shaft 11, and a second end engaged with a recessed
portion 17b which is recessed radially outward from the inner
circumferential surface of driven gear 17. Thus, drive pin 10b is
arranged to prevent the rotation of drive gear 16 relative to drive shaft
10, and to cause the drive gear 16 to rotate as a unit with drive shaft
10. When drive shaft 10 is driven, drive gear 16 rotates in accordance
with the rotation of drive gear 16 in the same direction as drive shaft
10. On the other hand, driven pin 11b is arranged to prevent the rotation
of driven gear 17 relative to driven shaft 11, and to cause the driven
gear 17 to rotate as a unit with driven shaft 11. Consequently, driven
gear 17 rotates with the driven shaft 11 in a direction opposite to the
rotational direction of drive shaft 10.

[0048]As shown in FIGS. 12 and 13, tooth tops 16a and 17a of gears 16 and
17 abuts slidably and liquid-tightly on tooth top seal portions 14g and
14h of seal block 14e of first side plate 14. Seal member 7 includes the
pair of R-portions 7e and 7f located on the rear surface of seal member
7. R-portions 7e and 7f of seal member 7 are engaged, respectively, with
the engagement portions 14i of tooth top seal portions 14g and 14h of
seal block 14e of first side plate 14, so that tooth tops of 16a and 17a
of gears 16 and 17 are sealed with side seal portion 14d of first side
plate 14. Moreover, a substantially triangular holding member 19 is fit
in groove 14j formed on the outer circumference of seal block 14e and on
the corresponding side seal portion 7d of seal member 7. On the other
hand, second pump 9 includes a second gear 23 having a front surface and
a rear surface sealed by seal member 7 and second side plate 22. Second
pump 9 has a structure symmetrical to first pump 8 with respect to seal
member 7. Structures of second side plate 22, second gear 23 and so on
have bilaterally symmetrical structures to first side plate 14, first
gear 15 and so on. Therefore, repetitive explanations are omitted as to
similar component parts to which the same reference numerals are given.

[0049]First pump chamber P1 includes a suction port (not shown) connected
with through hole 14c of first side plate 14, and formed on an inner wall
of pump chamber 4, and a discharge port (not shown) connected with a
space O1 (cf. FIGS. 3 and 4) of first pump chamber P1, and formed on the
inner wall of pump chamber 4. On the other hand, second pump chamber P2
includes a suction port (not shown) connected with a through hole (not
shown) of second side plate 22, and formed on the inner wall of pump
chamber 4 through a passage (not shown) of cover member 6, and a
discharge port (not shown) formed on cover member 6, and formed on the
inner wall of pump chamber 4 through a passage (not shown) of cover
member 6. Drive shaft 10 includes a mounting raised portion 10d which has
a substantially rectangular column, and which is formed at a front end
portion of drive shaft 10. Mounting raised portion 10d is mounted in a
mounting recessed portion 21a of a rotational shaft 21 of motor 20 which
is a driving source, so that a gear pump 1 is connected with motor 20.

[0050][Seal Section, Support Section and Urging Section of Drive Shaft]
Next, a seal section, a support section and an urging section are
illustrated. As shown in FIGS. 15 and 16, receiving portion 7g of seal
member 7 receives a shaft seal 30, a first bearing member 31, a second
bearing member 32 and a spring member 33. Shaft seal 30 serves as the
seal section. In the gear pump according to the first embodiment, shaft
seal 30 is an annular X-ring made of soft elastic material such as rubber
and resin. Shaft seal 30 is disposed to be pushed toward second pump 9 by
first bearing member 31. With this, the inner circumferential surface of
shaft seal 30 contacts the outer circumferential surface of drive shaft
10 to secure a seal separation between the first pump 8's side and the
second pump 9's side. First bearing member 31 serves as the support
section of drive shaft 10. In the gear pump according to the first
embodiment, first bearing member 31 is a cylindrical metal bush made of a
cemented carbide or hard metal made of a sintered material and so on.
Second bearing member 32 has an inside diameter slightly larger than an
outside diameter of drive shaft 10. Second bearing member 32
liquid-tightly supports drive shaft 10 by the hydraulic fluid on the
first pump 8's side.

[0051]Second bearing member 32 serves as the support section and the
urging section of drive shaft 10. Second bearing member 32 includes a
pair of confronting walls 32a which are disposed on the outer
circumference surface of second bearing member 32, and which protrude
outwards. Between the confronting walls 32a, there is provided spring
member 33 formed by bending a metal sheet into a substantially U-shape as
shown in FIG. 17. As shown in FIG. 18, spring member 33 is retained in
retaining recessed portion 7j of receiving portion 7g to prevent the
rotation of second bearing member 32 relative to seal member 7. As
mentioned above, retaining recessed portion 7j of receiving portion 7g is
located at a position to confront R-portion 7e. Accordingly, second
bearing member 32 is urged by the urging force of spring member 33 toward
R-portion 7e of seal member 7. Therefore, second bearing member 32 is
mounted in an eccentric state on a smaller diameter portion 10c of drive
shaft 10, and positioned in the axial direction. Second bearing member 32
urges drive shaft 10 toward R-portion 7e so that drive shaft 10 is
slightly eccentric. Accordingly, as shown in FIG. 19, tooth top 16a of
drive gear 16 of each gear 15 or 23 mounted to drive shaft 10 is disposed
to always protrude outside the corresponding R-portion 7e of the front or
rear surface of seal member 7, as shown by a two-dot chain line
indicative of a diameter of the circle of the tooth top 16a. Therefore,
tooth top 16a of drive gear 16 is urged to contact tooth top seal portion
14g. That is, drive shaft 10 does not contact the inner circumferential
surface of shaft hole 7a. Drive shaft 10 is urged from the center of
second bearing member 32 toward tooth top seal member 14g to be eccentric
from the center of second bearing member 32. Drive shaft 10 is
liquid-tightly and rotatably supported to be slid on a part of the inner
circumferential surface of first bearing member 31 and a part of the
inner circumferential surface of second bearing member 32. In FIG. 19,
tooth top 16a protrudes largely from R-portion 7e to facilitate the
understanding of the eccentric direction of drive shaft 10. However,
actual protruding amount of tooth top 16a, that is, the eccentric amount
of drive shaft 10 is set equal to or smaller than, for example, 1 mm.
Similarly, a clearance between drive shaft 10 and bearing hole 7a is
actually small.

[0052][Assembly Operation of Gear Pump] Next, an assembly operation of
gear pump 1 is illustrated. The thus-constructed gear pump 1 is assembled
in the following manner. First, drive shaft 10 is inserted into shaft
hole 7a of seal member 7 preliminary equipped with seal S4. Then, shaft
seal 30 and first bearing member 31 are inserted into receiving portion
7g, and mounted on drive shaft 10. Then, second bearing member 32 is
inserted into receiving portion 7g to adjust the positions in the
rotational direction of the pair of confronting walls 32a and retaining
recessed portion 7j, and spring member 30 is mounted in retaining
recessed portion 7j. In this case, drive shaft 10 is urged to R-portion
7e by the urging force of spring member, so that drive shaft 10 is
eccentric. The rotation of second bearing member 32 is prevented by
spring member 30. Next, driven shafts 11 are inserted, respectively, into
shaft holes 7b of seal member 7. Next, drive pins 10b and driven pins lib
are inserted, respectively, into recessed portions 10a of drive shaft 10
and recessed portions 11a of driven shaft 11. Next, drive gears 16 and
driven gears 17 of gears 15 and 23 are assembled, respectively, to drive
shaft 10 and driven shaft 11.

[0053]Next, drive shaft 10 and driven shaft 11 are inserted, respectively,
into side plates 14 and 22 preliminary equipped with seal S5 and holding
member 19, so that side plates 14 and 22 are assembled to seal member 7.
In this case, drive gears 16a of gears 15 and 23 are urged to contact
tooth top seal portions 14g of side plates 14 and 22. On the first side
plate 14's side of seal member 7, the pair of R-portions 7e and 7f are
engaged, respectively, with engagement portions 14i to position these
components. Holding member 19 can temporarily hold and fix seal member 7
and first side plate 14. Holding member 16 can be readily mounted on seal
member 7 and first side plate 14 by first mounting the holding member 16
on seal member 7, and then expanding holding member 16 onto first side
plate 14. Similarly, in the second side plate 22, it is also possible to
obtain the same effect by holding member 19.

[0054]Next, drive shaft 10 is inserted into through hole 6a of cover
member mounted in advance with seals S1 and S2. Annular protrusion 6c of
cover member 6 is fit over (on) seal member 7 to assemble cover member 6
and seal member 7. Consequently, pump assembly 3 is temporarily
assembled.

[0055]Next, the temporarily assembled pump assembly 3 is inserted into
pump chamber 4 of housing 2. Then, plug member 5 is screwed into and
fixed to pump chamber 4. In this case, seal member 7 contacts stepped
portion 4b of pump chamber 4 by the axial force produced by screwing plug
member 5, and seal member 4 can be stably fixed. The front and rear
positions of components can be accurately positioned. Accordingly, it is
possible to prevent unsteadiness or shakiness due to the variation of the
pressure of the hydraulic fluid as mentioned later.

[0056]Moreover, seal S1 is pressed by annular protrusion 5b of plug member
5. Therefore, it is possible to improve the sealing ability between pump
chamber 4 and cover member 6. In this way, in the gear pump 1 according
to the first embodiment, the temporarily assembled pump assembly 3 can be
received into housing 2. Therefore, it is possible to simplify the
assembly operation.

[0057][Operation of Gear Pump] Next, the operation of gear pump 1 is
illustrated. In gear pump 1, when drive shaft 10 is driven and rotated by
the rotation of rotation shaft 21 of motor 20, driven gear 17 of first
pump 8 is driven and rotated by the rotation of drive gear 16, as shown
in FIG. 11. By this operation, the hydraulic fluid of the low pressure is
introduced from through hole 14c of seal block 14e of first side plate 14
which is connected with the suction port. The hydraulic fluid of the high
pressure is outputted to region O1 of first pump chamber P1. The
hydraulic fluid of the high pressure is outputted from the corresponding
discharge port. A circumference space of through hole 14c from which the
hydraulic fluid is sucked by the rotations of gears 16 and 17 becomes a
suction portion B1 which is the low pressure side. Space O1 (cf. FIGS. 3
and 4) to which the hydraulic fluid is discharged by the rotations of
gears 16 and 17 becomes a discharge portion B2 which is the high pressure
side. In second pump 9, driven gear 17 is driven through drive gear 16 of
second gear 23 in accordance with the rotation of first pump 8, like
first pump 8, and second pump 9 is operated like first pump 8. In this
way, first gear pump 1 can perform the suction operations and the
discharge operations of the hydraulic fluid in the two separate hydraulic
systems in pump chambers P1 and P2. Gear pump 1 can function as a tandem
external gear pump. In general, the hydraulic fluid in the first system
which is introduced into first pump chamber P1 corresponds to a brake
circuit of one of a left front wheel and a right rear wheel of a vehicle,
and a right front wheel and a left rear wheel of the vehicle. The
hydraulic fluid in the second system which is introduced into second pump
chamber P2 corresponds to a brake circuit of the other of the left front
wheel and the right rear wheel of the vehicle, and the right front wheel
and the left rear wheel of the vehicle.

[0058][Seal of Tooth Top] In the gear pump according to the first
embodiment, suction portion B1 from which the hydraulic fluid is sucked
is the low pressure, and discharge portion B2 to which the hydraulic
fluid is discharged is the high pressure. Accordingly, tooth tops 16a and
17a of gears 16 and 17 are pushed, respectively, to the tooth top seal
portions 14g and 14h of seal block 14e by the pressure difference between
suction portion B1 and discharge portion B2, so that tooth tops 16a and
17a are liquid-tightly abutted on and slid on tooth top seal portions 14g
and 14h of seal block 14. Therefore, it is possible to ensure the seal
ability of tooth tops 16a and 17a of gears 16 and 17, that is, the
sealing separation between the high pressure side and the low pressure
side.

[0059]In the conventional gear pump, the sufficient pressure difference
between the suction portion and the discharge portion is not obtained at
the start of the driving of the gear pump. Accordingly, the tooth top of
the drive gear can not be sufficiently pressed on (against) the seal
surface at the start of the driving of the gear pump, and the tooth top
of the drive gear can not contact the seal surface. Therefore, it is not
possible to smoothly increase the pressure of the gear pump. Moreover,
the unsteadiness or shakiness is caused due to the error of the
manufacturing accuracy or the error of the assembly accuracy of the drive
shaft and the bearing, the drive shaft and the gear, and the peripheral
members. Accordingly, the protruding amount of the tooth top of the drive
gear from the R-portion 7e increases or decreases. For example, in a case
in which the protruding amount of the tooth top 16a of drive gear 16 from
R-portion 7e is small, the clearance is generated between tooth top 16a
of drive gear 16 and tooth top seal portion 14g. Consequently, it is not
possible to ensure the sealing ability of tooth top 16a of drive gear 16.

[0060]Moreover, two pumps 8 and 9 use single drive shaft 10 in the first
embodiment. In this case, when the pressures of the hydraulic fluid of
the pumps 8 and 9 are different, the forces acted to pumps 8 and 9 are
different. For example, in a case in which the discharge pressure is
largely acted to first pump 8 and the first gear 15 and drive shaft 10
are moved to the low pressure side, drive shaft 10 moves to the low
pressure side. In this case, there is no problem if the first pump 8's
side and the second pump 9's side of drive shaft 10 are equally moved to
the low pressure side. However, in fact, the only first pump 8's side of
drive shaft 10 is moved to the low pressure side, so that drive shaft 10
is inclined from a horizontal line X1 shown in FIG. 16 to a line X2 shown
in FIG. 16. This inclination of drive shaft 10 causes the movement
(displacement) in the opposite direction on the second pump 9's side of
drive shaft 10. Consequently, the seal ability of tooth top 16a of drive
gear 16 may be deteriorated in second pump 9. Moreover, when drive shaft
10 is inclined, the smooth rotation between drive shaft 10 and first
bearing member 31, and between drive shaft 10 and second bearing member
32 are inhibited, so that the friction increases. That is, when drive
shaft 10 is inclined due to one of first pump 8 and second pump 9, the
seal ability may be deteriorated in the other of first pump 8 and second
pump 9, and the friction may be increased in the entire gear pump 1.

[0061]In the gear pump according to the first embodiment, drive shaft 10
is eccentric to tooth top seal portion 14g. Tooth tops 16a of drive gear
16 are constantly urged to contact tooth top seal portion 14g.
Consequently, tooth tops 16a can be slid while strongly (mightily)
abutted on tooth top seal portion 14g. Accordingly, it is possible to
ensure the good seal ability of tooth top 16a, irrespective of the
pressure difference of the hydraulic fluid or the existence or
nonexistence of the pressure. Specifically, this is advantageous to the
brake fluid with the low viscosity. Moreover, tooth tops 17a of driven
gear 17 can attain the good contact with tooth top seal portion 14h since
driven gear 17 is engaged with drive gear 16, and rotated with drive gear
16. It is possible to improve the seal ability of tooth top 17a of driven
gear 17. Accordingly, it is possible to sufficiently increase the
pressure of gear pump 1 at the start of the driving of gear pump 1 at
which the pressure difference of the hydraulic fluid is small. Moreover,
gear pump 1 of the first embodiment is used as an actuator for
controlling the pressure of the brake fluid of the vehicle. Accordingly,
it is possible to improve the brake performance. For example, it is
possible to attain the good brake control with the good brake pressure
increase at the operation of the VDC (vehicle dynamics control), and to
further stabilize the vehicle motion (behavior). In a case in which tooth
tops 16a are flush with R-portion 7e of seal member 7 or tooth top 16a is
positioned radially inside R-portion 7e of seal member 7, tooth tops 16a
and tooth top seal portion 14g are not slid on each other in the state in
which tooth top 16a and tooth top seal portion 14g are strongly abutted
on each other. Consequently, it is not possible to ensure the good seal
ability. That is, tooth tops 16a are slid in the state in which the tooth
tops 16a are strongly abutted on tooth top seal portion 14g, and
consequently it is possible to attain the good seal between the high
pressure side and the low pressure side.

[0062][Prevention of Inclination of Drive Shaft] In gear pump 1 according
to the first embodiment, drive shaft 10 can be constantly positioned on
tooth top seal portion 14g's side. Accordingly, even when the error of
the manufacturing accuracy or the error of the assembly accuracy of drive
shaft 10 and the peripheral members are generated, it is possible to
prevent the inclination of drive shaft 10. Therefore, the inclination of
drive shaft 10 generated in one of pump 8 and pump 9 does not cause the
adverse effect on the other of pump 8 and pump 9. In addition, the smooth
rotation of drive shaft 10 and first bearing member 31, and the smooth
rotation of drive shaft 10 and second bearing member 32 are not
inhibited. Accordingly, it is possible to suppress the increase of the
friction.

[0063][Prevention of Seizing of Drive Shaft] Moreover, it is possible to
decrease a contact area between drive shaft 10 and first bearing member
31 (second bearing member 32) supporting drive shaft 10. Accordingly, it
is possible to prevent the seizing by the rotation of drive shaft 10.
Moreover, it is possible to improve the transmission efficiency of the
driving force of motor 20 since the frictional resistance of drive shaft
10 decreases.

[0064][Size Reduction and Weight Reduction of Periphery of Drive Shaft] In
the gear pump according to the first embodiment, first bearing member 31
is the cylindrical metal bush. Accordingly, it is possible to attain the
size reduction and the weight reduction of gear pump 1, relative to the
gear pump employing another bearing member such as a needle bearing.
Moreover, second bearing member 32 is fit on smaller diameter portion 10c
of drive shaft 10 in the eccentric state. Therefore, it is possible to
readily ensure the space in which spring member 33 is disposed, and to
decrease the size and the weight of gear pump 1 without increasing the
size of the peripheral members in the radial direction by spring member
33.

[0065](1) A gear pump according to the embodiments of the present
invention includes: a drive shaft (10) driven by a driving source (20); a
first gear (15) arranged to rotate integrally with the drive shaft (10),
and to form a first pump (8), the first gear (15) having a first surface
and a second surface opposite to the first surface of the first gear
(15); a second gear (23) arranged to rotate integrally with the drive
shaft (10), and to form a second pump (9), the second gear (23) having a
first surface and a second surface opposite to the first surface of the
second gear (23); a first plate (7) disposed between the first gear (15)
and the second gear (23), and arranged to liquid-tightly seal the first
surface of the first gear (15), and to liquid-tightly seal the first
surface of the second gear (23); a pair of second plates (14,22)
disposed, respectively, on the second surface of the first gear (15) and
the second surface of the second gear (23), and arranged to
liquid-tightly seal the second surface of the first gear (15) and the
second surface of the second gear (23), each of the second plates (14,22)
including a tooth top sealing portion (14e) having a seal surface (14g)
arranged to seal a tooth top (16a) of the first gear (15) and a tooth top
(16a) of the second gear (23), and to form a suction portion (B1) with
the first plate (7) and the second plate (14,22); and an urging member
arranged to urge the drive shaft (10) toward the seal surface (14g) of
the tooth top sealing portion (14e) of one of the first and second
plates. Accordingly, it is possible to smoothly increase the pressure by
sealing tooth tops 16a and 17a of gears 15 and 23 even when the
sufficient pressure difference between suction portion B1 and discharge
portion B2 of the hydraulic fluid. Moreover, it is possible to prevent
the inclination of drive shaft 10, and to suppress the increase of the
friction.

[0066](2) In the gear pump according to the embodiments of the present
invention, the first plate (7) includes a through hole (7a) through which
the drive shaft (10) penetrates; the drive shaft (10) is supported
through a bearing member (31) by the through hole (7a) of the first plate
(7); and the urging section is provided within the through hole (7a) of
the first plate (7). Accordingly, it is possible to support drive shaft
10 by the bearing member (first bearing member 31), irrespective of the
strength, the material and so on of shaft hole 7a of the first plate
(seal member 7), and to expand the freedom of the design of the first
plate (seal member 7). Moreover, it is possible to attain the size
reduction and the weight reduction, relative to a gear pump in which the
urging section is provided outside the first plate (seal member 7).

[0067](3) In the gear pump according to the embodiments of the present
invention, the urging section is arranged to urge the drive shaft (10) so
that the drive shaft (10) has a center deviated from a center of the
bearing member (31). Accordingly, it is possible to prevent the seizing
by the rotation of drive shaft 10, and to improve the durability.

[0068](4) In the gear pump according to the embodiments of the present
invention, the drive shaft (10) includes a bearing member mounting
portion (a part of the outer circumference surface of drive shaft 10)
located on an outer circumference surface of the drive shaft (10), and
arranged to receive the bearing member (31), and an urging member
mounting portion (10c) arranged to receive the urging member. The
thus-constructed gear pump can provide the same advantageous effects and
operations as in (2) and (3).

[0069](5) In the gear pump according to the embodiments of the present
invention, the urging member mounting portion includes an urging member
fitting portion (10c) formed by decreasing a diameter of the drive shaft
(10). Accordingly, it is possible to readily ensure a space in which the
urging member is disposed, and to attain the size reduction and the
weight reduction of gear pump 1.

[0070](6) In the gear pump according to the embodiments of the present
invention, the gear pump further includes a second bearing member (32)
which supports the drive shaft (10), and which is fit in the urging
member fitting portion (10c), and positioned in an axial direction so
that the second bearing member (32) has a center deviated from the center
of the drive shaft (10); the urging member is a spring member (33)
arranged to urge the drive shaft (10) through the second bearing member
(32) toward the seal surface (14g) of the tooth top seal member (14e).
Accordingly, it is possible to urge drive shaft 10 toward the seal
surface (tooth top seal portion 14g) by the simple structure.

[0071](7) In the gear pump according to the embodiments of the present
invention, the second bearing member (32) is positioned by the spring
member (33) in the through hole (7a) in the rotational direction.
Accordingly, it is possible to retain second bearing member 32 to prevent
the rotation, and to readily position the urging direction of drive shaft
10.

[0072](8) A gear pump according to the embodiments of the present
invention for a brake apparatus, the gear pump includes: a drive shaft
(10) driven by a driving source; a first gear (15) formed integrally with
the drive shaft (10), and arranged to rotate with the drive shaft, and to
form a first pump (8), the first gear (15) being provided in a first
brake circuit, and having a first surface and a second surface opposite
to the first surface of the first gear; a second gear (23) formed
integrally with the drive shaft (10), and arranged to rotate with the
drive shaft, and to form a second pump (9), the second gear (23) being
provided in a second brake circuit, and having a first surface and a
second surface opposite to the first surface of the second gear; a seal
plate (7) disposed between the first gear (15) and the second gear (23),
the seal plate (7) including a through hole (7a) through which the drive
shaft (10) penetrates, the seal plate (7) being arranged to suppress a
leakage of a brake fluid from the first surface of the first gear (15)
and a leakage of a brake fluid from the first surface of the second gear
(23); a pair of side plates (14,22) disposed, respectively, adjacent to
the second surface of the first gear (15) and the second surface of the
second gear (23), and arranged to suppress the leakage of the brake fluid
from the second surface of the first gear (15) and the leakage of the
brake fluid from the second surface of the second gear (23); a tooth top
sealing member (14e) including a seal surface (14g) arranged to seal a
tooth top (16a) of the first gear (15) and a tooth top (17a) of the
second gear (23), and defining a low pressure portion (B1) with the seal
plate (7) and the side plate (14,22); a bearing member (31) mounted in
the through hole (7a) of the seal plate (7), and arranged to support the
drive shaft (10); and an urging member arranged to urge the drive shaft
(10) so that a center of the drive shaft (10) is eccentric in a direction
from a center of the bearing member (31) to the seal surface (14g) of the
tooth top sealing portion (14e). The thus-constructed gear pump can
provide the same advantageous effects and operations as in (1).

[0073](9) In the gear pump according to the embodiments of the present
invention, the drive shaft includes a bearing member mounting portion (a
part of the outer circumference surface of drive shaft 10) disposed on an
outer circumference of the drive shaft (10), and arranged to receive the
bearing member (31), and an urging member mounting portion (10c) arranged
to receive the urging member; the urging member mounting portion includes
an urging member fitting portion (10c) formed by decreasing a diameter of
the drive shaft (10); and gear pump further includes a second bearing
member (32) which supports the drive shaft (10), and which is fit in the
urging member fitting portion (10c), and positioned in an axial direction
so that the second bearing member (32) has a center deviated from the
center of the drive shaft (10); and the urging member is a spring member
(33) arranged to urge the drive shaft (10) through the second bearing
member (32) toward the seal surface (14g) of the tooth top sealing
portion (14e). The thus-constructed gear pump can provide the same
advantageous effects and operations as in (2)-(5).

[0074](10) In the gear pump according to the embodiments of the present
invention, the gear (15,23) includes a drive gear (16) arranged to be
driven by the drive shaft (10), and a driven gear (17) engaged with the
drive gear (16), and arranged to be driven by the drive gear (16); and
the gear (15,23) is an external gear. Accordingly, the present invention
is applicable to the general external gear pump, and it is possible to
expand the general versatility. Moreover, it is possible to improve the
seal ability of tooth top 17a of driven gear 17.

Second Embodiment

[0075]Next, a gear pump according to a second embodiment of the present
invention is illustrated. The following explanation is directed only to
points different from the first embodiment, and repetitive explanation is
omitted as to similar component parts to which the same reference
numerals are given. FIG. 21 is an enlarged view showing a seal section, a
support section and an urging section of a gear pump according to a
second embodiment of the present invention. As shown in FIG. 21, in gear
pump 1 according to the second embodiment, shaft hole 7a has an enlarged
diameter substantially identical to the diameter of receiving portion 7g,
and penetrates through seal member 7. First bearing member 31 is disposed
at a central position between gears 15 and 23. First bearing member 31
includes a recessed portion 31a formed on an inner circumference surface
of first bearing member 31, and recessed in the radially outward
direction. Recessed portion 31a of first bearing member 31 receives shaft
seal 30. On the second gear 23's side, there are provided the support
section and the urging section (smaller diameter portion 10c, second
bearing member 32 and spring member 33) of drive shaft 10. Accordingly,
in the second embodiment, it is possible to attain the same effect as the
first embodiment. Moreover, it is possible to further restrict the
inclination of drive shaft 10, and to urge drive gear 16 toward tooth top
seal portion 14g from the both sides of the axial direction in the stable
state. Therefore, it is possible to further improve the seal ability of
tooth top 16a of drive gear 16 (tooth top 17a of driven gear 17).

[0076](11) In the gear pump according to the embodiments of the present
invention, the gear pump further includes a pair of the urging members
each arranged to urge the drive shaft (10) toward the seal surface (14g)
of the tooth top sealing portion (14e) of one of the second plates; and
the drive shaft (10) includes a bearing member mounting portion (parts of
the outer circumference surface of drive shaft 10 on the both sides)
disposed on an outer circumference of the drive shaft (10), and arranged
to receive the bearing member (31), and a pair of urging member mounting
portions (10c) disposed on both sides of the bearing member mounting
portion, and each arranged to receive one of the urging members (32,33).
Accordingly, it is possible to urge drive shaft 10 from the both sides of
the axial direction toward tooth top seal portion 14g in the stable
state, and to further improve the seal ability of tooth top 16a of drive
gear 16 (tooth top 17a of driven gear 17).

[0077](12) In the gear pump according to the embodiments of the present
invention, the gear pump further includes a pair of second bearing
members each of which supports the drive shaft, and each of which is fit
in one of the urging member fitting portions (10c), and positioned in an
axial direction so that the second bearing member (32) has a center apart
from the center of the drive shaft (10); and each of the urging members
is a spring member (33) arranged to urge the drive shaft (10) through the
second bearing member (32) toward the seal surface (14g) of the tooth top
sealing portion (14e). The thus-constructed gear pump can provide the
same advantageous effects and operations (6).

Third Embodiment

[0078]Next, a gear pump according to a third embodiment of the present
invention is illustrated. The following explanation is directed only to
points different from the first or second embodiment, and repetitive
explanation is omitted as to similar component parts to which the same
reference numerals are given. FIG. 22 is an enlarged view showing a seal
section, a support section and an urging section of a gear pump according
to a third embodiment of the present invention. In the gear pump
according to the third embodiment, shaft hole 7a of seal member 7 serves
as the support section of drive shaft 10, as shown in FIG. 22.
Accordingly, seal member 7 is made of cemented carbide or hard metal such
as the sintered metal and so on which is used as a sliding bearing
member. Moreover, the gear pump includes a shaft seal 26 which serves as
the seal section and the urging section of drive shaft 10, and which is
received in an annular holding groove 25 having an annular stepped
portion 25a. A washer ring 27 is fit in annular stepped portion 25a.
Drive pin 10b is abutted on washer ring 27, so that drive shaft 10 is
positioned in the axial direction. Moreover, another washer ring 27 is
mounted on the second pump 9's side, so that drive shaft 10 is positioned
in the axial direction in the same manner. The center of the inner
circumference surface of holding groove 25 is deviated from the center of
shaft hole 7a in a direction toward tooth top seal portion 14g (R-portion
7g). Accordingly, drive shaft 10 receives an urging (straining) force
from shaft seal 26 received in holding groove 25, in a direction toward
the center of shaft seal 26. Therefore, drive shaft 10 is disposed in a
state in which drive shaft 10 is urged toward tooth top seal portion 14g.
Consequently, tooth top 16a of drive gear 16 is urged to contact tooth
top seal portion 14g, like the first embodiment. Accordingly, the gear
pump according to the third embodiment can attain the same effects as the
gear pump according to the first embodiment. In addition, drive shaft 10
can be urged by the shaft seal member necessary for drive shaft 10,
without another member for positioning. Therefore, it is possible to
attain the size reduction and the weight reduction of gear pump 1, and to
decrease the number of the components.

[0079](13) In the gear pump according to the embodiments of the present
invention, the gear pump further includes a shaft seal member (26)
disposed in the through hole (7a) of the first plate (7), and arranged to
liquid-tightly seal between a first pump's side of the through hole (7a)
and a second pump's side of the through hole (7a); and the through hole
(7a) of the first plate (7) includes an annular holding groove (25)
having a center deviated from a center of the through hole (7a), and
supporting the shaft seal member (26); and the urging section is the
shaft seal member (26). The thus-constructed gear pump can provide the
same advantageous effects and operations. Moreover, it is possible to
urge drive shaft 10 by the shaft seal member necessary for drive shaft
10.

Fourth Embodiment

[0080]Hereinafter, a gear pump according to a fourth embodiment is
illustrated. The following explanation is directed only to points
different from the first to third embodiments, and repetitive explanation
is omitted as to similar component parts to which the same reference
numerals are given. FIG. 23 is a view showing an urging section of drive
shaft 10 of a gear pump according to a fourth embodiment of the present
invention. As shown in FIG. 23, in the gear pump according to the fourth
embodiment, seal member 7 includes a cutaway portion 28 which is cut in
the radially outward direction from shaft hole 7a at a position to
confront R-portion 7e. A metal ball 29 is inserted into and mounted in
cutaway groove 28 by the press fit, and metal ball 29 is abutted on drive
shaft 10 to urge drive shaft 10 toward tooth top seal portion 14g.
Consequently, tooth top 16a of drive gear 16 is urged to contact tooth
top seal portion 14g, like the first embodiment. Metal ball 29 may be
substituted by an elastic member such as a spring, a rubber resin and so
on. Accordingly, in the gear pump according to the fourth embodiment, it
is possible to form the urging section of drive shaft 10 by the simple
structure.

[0081](14) In the gear pump according to the embodiments of the present
invention, the gear pump further includes a pressing member (29) which is
the urging member, which is disposed in an inner circumference surface of
the through hole (7a) of the first plate (7), and which is arranged to
press the drive shaft (10) to the seal surface (14g) of the tooth top
sealing portion (14e). Accordingly, it is possible to form the urging
section of drive shaft 10 by the simple structure.

[0082](15) In the gear pump according to the embodiments of the present
invention, the pressing member is a press-fitting member (29) which is
press-fit in the inner circumference surface of the through hole (7a) of
the first plate (7). Accordingly, it is possible to readily mount the
pressing member (metal ball 29).

Fifth Embodiment

[0083]Hereinafter, a gear pump according to a fifth embodiment is
illustrated. The following explanation is directed only to points
different from the first to fourth embodiments and repetitive explanation
is omitted as to similar component parts to which the same reference
numerals are given. FIG. 25 is a sectional view showing a gear pump
according to a fifth embodiment of the present invention. In the first
embodiment, the gear pump is the tandem external gear pump. In the fifth
embodiment, the gear pump is a single external gear pump, as shown in
FIG. 24. That is, the gear pump has no components of second pump 9, and
the gear pump includes first gear pump 8 only. Seal member 7 has a
smaller width in the forward and rearward directions. Seal member 7 is
formed integrally with cover member 6 to form single seal member 7.
Accordingly, in the fifth embodiment, it is possible to attain the same
effects as the first embodiment. In the fifth embodiment, the seal
section, the support section and the urging section have the same
structures as the seal section, the support section and the urging
section of the first embodiment. However, the seal section, the support
section and the urging section may have the same structures as the seal
section, the support section and the urging section of the second or
third embodiment.

[0084](16) A gear pump according to the embodiments of the present
invention includes: a drive shaft (10) driven by a driving source (20); a
gear (15) disposed in a pump chamber (P1) formed in a housing (2), and
arranged to be driven by the drive shaft (10), and to form a pump; a
plate (7) disposed adjacent to a surface of the gear (15), and arranged
to suppress a leakage of a hydraulic fluid from the surfaces of the gear
(15); a tooth top seal member (14e) including a seal surface (14g)
abutted on the plate (7), and arranged to seal a tooth top (16a) of the
gear (15), and to separate the pump chamber (P1) into a low pressure
portion (B1) and a high pressure portion (B2); and an urging member
arranged to urge the drive shaft (10) toward the seal surface (14g) of
the tooth top seal member (14e). The thus-constructed gear pump can
provide the same advantageous effects and operations as in (1).

[0085](17) In the gear pump according to the embodiments of the present
invention, the plate (7) includes a holding hole (7a) arranged to hold
the drive shaft (10); and the urging member is disposed in the holding
hole (7a) of the plate (7). The thus-constructed gear pump can provide
the same advantageous effects and operations as in (1).

[0086](18) In the gear pump according to the embodiments of the present
invention, the urging member is supported through a bearing member (32)
by the holding hole (7a) of the plate (7); and the urging member is
arranged to urge the drive shaft (10) so that the drive shaft (10) has a
center deviated from a center of the bearing member (32). The
thus-constructed gear pump can provide the same advantageous effects and
operations as in (3).

[0087](19) In the gear pump according to the embodiments of the present
invention, the drive shaft (10) includes a bearing member mounting
portion (a part of the outer circumference surface of drive shaft 10)
disposed on an outer circumference surface of the drive shaft (10), and
arranged to receive the bearing member (31), and an urging member
mounting portion (10c) arranged to receive the urging member; and the
drive shaft (10) is positioned by the urging member mounting portion
(10c) with respect to the plate (7) in the axial direction. The
thus-constructed gear pump can provide the same advantageous effects and
operations as in (4).

[0088](20) In the gear pump according to the embodiments of the present
invention, the urging member mounting portion includes an urging member
fitting portion (10c) formed by decreasing a diameter of the drive shaft
(10); and the gear pump further includes a second bearing member (32)
which supports the drive shaft, which is fit in the urging member fitting
portion (10c), and positioned in the axial direction so that the second
bearing member (32) has a center apart from the center of the drive shaft
(10); and the urging member is a spring member (33) arranged to urge the
drive shaft (10) through the second bearing member (32) toward the seal
surface (14g) of the tooth top sealing member (14e). The thus-constructed
gear pump can provide the same advantageous effects and operations as in
(5) and (6).

Sixth Embodiment

[0089]Hereinafter, a gear pump according to a sixth embodiment is
illustrated. The following explanation is directed only to points
different from the first to fifth embodiments, and repetitive explanation
is omitted as to similar component parts to which the same reference
numerals are given. FIG. 25 is a view showing a gear pump according to a
sixth embodiment of the present invention. As shown in FIG. 25, in the
gear pump according to the sixth embodiment, driven shafts 11 of gears 15
and 23 are integrally formed to one driven shaft 11. Driven shaft 11 is
provided with a seal section, a support section and an urging section,
like drive shaft 10, unlike the first embodiment. Accordingly, in
addition to the effects by the first embodiment, it is possible to
further improve the seal ability of tooth tops 17a of driven gears 17 of
gears 15 and 23, and to prevent the inclination of driven shaft 11. In
the gear pump according to the sixth embodiment, the seal section, the
support section and the urging section of drive gear 10 have the same
structures as the seal section, the support section and the urging
section of the first embodiment. However, the seal section, the support
section and the urging section of the gear pump according to the sixth
embodiment may have the same structures as the seal section, the support
section and the urging section of the gear pump of the second or third
embodiment.

Seventh Embodiment

[0090]Hereinafter, a gear pump according to a seventh embodiment is
illustrated. The following explanation is directed only to points
different from the first to sixth embodiments, and repetitive explanation
is omitted as to similar component parts to which the same reference
numerals are given. FIG. 26 is a view showing a gear pump according to a
seventh embodiment of the present invention. FIG. 27 is a sectional view
showing the gear pump of FIG. 26. FIG. 28 is a view showing the gear pump
of FIG. 26 when a suction and a discharge are changed. In the first
embodiment, gear pump 1 is the tandem type external gear pump. In the
seventh embodiment, gear pump 1 is a tandem type internal gear pump. As
shown in FIG. 26, each of side plates 14 and 22 has a U-shaped cross
section. Side plate 14 is symmetrical to side plate 22 with respect to
seal member 7. Side plate 14 and 22 are disposed to sandwich seal member
7, and the same reference numerals are given to similar component parts.
Each of side plates 14 and 22 includes an annular outer seal portion 41
which protrudes toward seal member 7, and each of which is formed on an
outer circumference portion of outer side plates 14 and 22. Each of outer
seal portion 41 is fit on the outer circumference portion of the
corresponding side seal portion 7d of seal member 7. First gear 15
forming first pump 8 is disposed in a space surrounded by seal member 7
and outer seal portion 41 of first side plate 14. On the other hand,
second gear 23 forming second pump 9 is disposed in a space surrounded by
seal member 7 and outer seal portion 41 of second side plate 22. Annular
seals S6 are mounted, respectively, on the outer circumference surfaces
of outer seal portions 41 to ensure the seal ability with seal member 7.

[0091]As shown in FIG. 27, first gear 15 includes an outer rotor having an
internally toothed portion 42a formed on an inner circumference surface
of outer rotor 42, and an inner rotor 43 having an externally toothed
portion 43a formed on the outer circumference surface of inner rotor 43.
Outer rotor 42 has a center deviated from a center of inner rotor 43. The
internally toothed portion 42a and the externally toothed portion 43a are
engaged, so that there is formed a pump chamber 44 surrounded by outer
rotor 42 and inner rotor 43. Drive shaft 10 includes a driving raised
portion 45 which is formed integrally with drive shaft 10, and which is a
rectangular column extending in the radial direction. This driving raised
portion 45 of drive shaft 10 is engaged with a recessed portion 43b which
is formed by cutting inner rotor 43. With this, inner rotor 43 is
retained to drive shaft 10 by driving raised portion 45 so as not to
rotate relative to drive shaft 10. When inner rotor 43 rotates, outer
rotor 42 is arranged to rotate in the same rotational direction as the
rotational direction of inner rotor 43. Moreover, outer rotor 42 is
arranged to rotate while slid on the inner circumference surface of outer
seal portion 41 of first side plate 14. Furthermore, first side plate 14
includes a suction opening 46 and a discharge opening 47 disposed at
positions to confront pump chamber 44. Each of suction opening 46 and
discharge opening 47 may have a substantially crescent groove. Suction
opening 46 is connected through a passage 48 formed in first side plate
14 shown in FIG. 26, to suction port 49 formed in the inner wall of first
pump chamber P1. Discharge opening 47 is connected through space O1 of
first pump chamber P1 to discharge port 50. On the other hand, second
gear 23 has a structure identical to the structure of first gear 15 of
first pump 8. A suction opening (not shown) of second side plate 22 is
connected through a passage 51 formed in second side plate 22 and a
passage 52 formed in cover member 6, to suction port 53 formed in the
inner wall of pump chamber 4. A discharge opening (not shown) of second
side plate 22 is connected from space O1 of second pump chamber P2
through a passage 54 formed in cover member 6, to discharge port 55
formed in the inner wall of second pump chamber P2. Seals S7 are mounted,
respectively, on the suction opening's side of side plate 14 and 22 to
secure a sealing separation between the high pressure side and the low
pressure side of pump chambers P1 and P2.

[0092]Drive shaft 10 is provided with the seal section, the support
section, and the urging section of drive shaft 10, like the first
embodiment. In the seventh embodiment, shaft hole 7a has an elongated
diameter identical to the diameter of receiving groove 7g to penetrate
through seal member 7. Moreover, first bearing member 32 has an elongated
axial length. However, the seal section, the support section and the
urging section of drive shaft 10 may have the same structures as the seal
section, the support section and the urging section of the second or
third embodiment. In the seventh embodiment, drive shaft 10 is urged by
the urging section of drive shaft 10 toward a seal portion 56 dividing
the high pressure side and the low pressure side of pump chamber 44, as
shown in FIG. 27. Consequently, externally toothed portion 43a of inner
rotor 43 is urged to contact internally toothed portion 42a of outer
rotor 42 at seal portion 56.

[0093][Operation of Gear Pump] Next, operation of the gear pump according
to the seventh embodiment is illustrated. In the thus-constructed gear
pump 1, when drive shaft 10 is rotated by motor 20 in the clockwise
direction of FIG. 27, outer rotors 42 are driven through inner rotors 43
in pumps 8 and 9. In this case, the pump operation (function) is
generated by the volume variations of pump chambers 44 of gears 15 and
18. In first pump 8, the hydraulic fluid of the low pressure is
introduced from suction port 46 of first side plate 14, and pressurized.
Then, the hydraulic fluid is outputted from discharge port 47 through
space O1 of first pump chamber P1 to discharge port 50. Similarly, in
second pump 9, the hydraulic fluid of the low pressure is introduced from
the suction port of second side plate 22, and pressurized. Then, the
hydraulic fluid is outputted from the discharge port through space O of
second pump chamber P2 to discharge port 55. In this way, in gear pump 1
according to the seventh embodiment, pumps 8 and 9 perform the suction
operations and the discharge operations of the hydraulic fluid in the two
separate hydraulic systems. That is, gear pump 1 serves as the tandem
internal gear pump. As mentioned above, drive shaft 10 is urged toward
seal portion 56, and accordingly it is possible to ensure the good seal
ability at seal portion 56.

[0094]In the gear pump according to the seventh embodiment, the suction
and the discharge of the hydraulic fluid of first and second pumps 8 and
9 are in the same direction. However, the suction and the discharge of
the hydraulic fluid of first and second pumps 8 and 9 may be in opposite
directions (180 degrees). In this case, there is provided an urging
section of drive shaft 10 to urge both sides of drive shaft 10 toward
seal portions 56 of first and second gears 15 and 23. In FIG. 28, the
seal section and support section of drive shaft 10 has the same
structures of the seal section and the support section as the second
embodiment. However, the seal section and the support section of drive
shaft 10 may have the same structures of the seal section and the support
section as the first embodiment, the third embodiment, or FIG. 26.

[0095]Although the embodiments of the present invention have been
described above, the invention is not limited to the embodiments
described above. Various forms and modifications are included as long as
they are not deviated from the gist of the invention. For example, it is
optional to change other material, other shapes, other numbers, other
sizes and so on of the constituent parts in the embodiments. Moreover,
spring member 33, metal ball 29 and elastic member 60a (described later)
may be substituted by various springs, rubbers, elastic members made of
resin, or a member formed by molding these members to a metal member.
Moreover, when the rotation direction of drive shaft 10 is reversed, the
hydraulic fluid flows from the discharge port to the suction port.

[0096]Moreover, as shown in FIG. 29, the support section and the urging
section of drive shaft 10 are formed by combining an elastic member 60a
which is a relatively soft rubber, resin or on, and a rigid backup ring
60b to reinforce elastic member 60a. Specifically, holding groove 25 of
the third embodiment is disposed at a substantially central position of
gears 15 and 23. Holding groove 25 receives backup ring 60b rotatably
supporting drive shaft 10, and elastic member 60a which urges drive shaft
10 through backup ring 60b toward tooth top seal portion 14g so that
drive shaft 10 becomes the eccentric state. The seal section of drive
shaft 10 is provided as another member. Moreover, it is optional to
provide either of the seal section or the support section of drive shaft
10 as the another member. The sectional shape of elastic member 60a may
be circular shape, rectangular shape, or X-shape in accordance with the
desired seal ability and the straining force (urging force).

[0097]Moreover, as shown in FIG. 30, backup ring 60b may have a
substantially U-shaped cross section which is opened outwards. Elastic
member 60a is provided in the U-shaped backup ring 60b. In this case, the
inner circumference surface of holding groove 25 is eccentric, like the
third embodiment. Alternatively, the groove of backup ring 60b on which
the inner circumference surface of shaft seal 60a is abutted is
eccentric. In this case, backup ring 60b is provided so as not to rotate.

[0098]Moreover, as shown in FIG. 31, it is optional to employ a rolling
bearing using a needle bearing 61a as the support section of drive shaft
10.

[0100]Although the invention has been described above by reference to
certain embodiments of the invention, the invention is not limited to the
embodiments described above. Modifications and variations of the
embodiments described above will occur to those skilled in the art in
light of the above teachings. The scope of the invention is defined with
reference to the following claims.